Field of the Invention
The present invention relates generally to an apparatus for and a method of producing a two-color molded article, and more particularly to an apparatus for and a method of advantageously producing a two-color molded article which consists of a primary molded body and a secondary molded body and in which the secondary molded body is superposed on the primary molded body such that the primary and secondary molded bodies are bonded together or not bonded together.
Discussion of Related Art
As one kind of resin molded articles, there is a two-color molded article consisting of a primary molded body molded by a primary injection molding operation using a first resin material and a secondary molded body molded by a secondary injection molding operation using a second resin material which is different from the first resin material. In the two-color molded article, the secondary molded body is superposed on the primary molded body such that the primary and secondary molded bodies are bonded together. The two-color molded article is used for components of a vehicle, an electric device, and various kinds of specifically designed products, for example. Recently, it is considered to produce a two-color molded article wherein the secondary molded body is superposed on the primary molded body such that the primary and secondary molded bodies are not bonded together.
In the production of the two-color molded article, an apparatus as disclosed in JP-A-2009-78436 is generally used. The apparatus disclosed in the above-described document comprises a turntable which is rotatable about an axis, first and second lower molds which have respective cavity surfaces of the same shape and which are located on the turntable, first and second upper molds which have respective cavity surfaces of different shapes and which are disposed so as to be movable toward and away from the first and second lower molds, an opening and closing device for moving the first and second upper molds toward and away from the first and second lower molds to close and open the upper and lower molds, and first and second injection units disposed such that their nozzles contact with the first and second upper molds at respective nozzle fitting portions provided on the first and second upper molds.
In the production of the two-color molded article by using the above-described apparatus, the first upper and lower molds are closed by the opening and closing device so as to form a primary molding cavity having a shape corresponding to the primary molded body between the first upper and lower molds. Then, the first resin material in a molten state is injected from the first injection unit so as to fill the primary molding cavity, and the first resin material filled in the primary molding cavity is solidified so as to obtain the primary molded body. The first upper and lower molds are opened by the opening and closing device such that the primary molded body is retained by the first lower mold. Then, the turntable is rotated so that the first lower mold retaining the primary molded body is positioned right below the second upper mold, and the second lower mold is positioned right below the first upper mold. Then, the second upper mold and the first lower mold are closed while the first upper mold and the second lower mold are closed, by the opening and closing device. Thus, a secondary molding cavity having a shape corresponding to the secondary molded body is formed between the second upper mold and the first lower mold with the primary molded body being retained inside the secondary molding cavity, while the primary molding cavity is formed between the first upper mold and the second lower mold. Then, the second resin material in a molten state is injected from the second injection unit so as to fill the secondary molding cavity while the first resin material in a molten state is injected from the first injection unit so as to fill the primary molding cavity. Thus, the secondary molded body is molded so as to be superposed on the primary molded body inside the secondary molding cavity whereby the desired two-color molded article is produced. On the other hand, another primary molded body is molded inside the primary molding cavity. After the two-color molded article is removed by opening the second upper mold and the first lower mold while opening the first upper mold and the second lower mold, the turntable is rotated. The above-described process is repeated.
By using the apparatus having the above-described conventional structure, it is possible to successively produce the desired two-color molded article. However, the conventional apparatus for producing the two-color molded article is configured such that the first and second injection units are disposed in spaces separate from the space in which the two pairs of forming molds (the first upper and lower molds and the second upper and lower molds) are disposed such that the nozzles of the injection units contact with the respective nozzle fitting portions of the first and second upper molds. Therefore, the conventional apparatus for producing the two-color molded article necessarily has an extremely larger size than a general injection molding apparatus having only one injection unit.
In the above-described situation, JP-A-2004-1403, for example, proposes an apparatus for producing the two-color molded article comprising one pair of forming molds and two injection units, wherein at least one of the two injection units is attached to the pair of forming molds. The apparatus makes it possible to reduce the space in which the injection unit attached to the pair of forming molds is disposed, as compared with that of the above-described conventional apparatus, thereby reducing the overall size of the apparatus.
However, the present inventors conducted various studies on the structure of the above-described apparatus for producing the two-color molded article, and found that the apparatus has the following potential problems.
In the apparatus for producing the two-color molded article configured such that the at least one of the first and second injection units is attached to the pair of forming molds, a primary molding cavity having a shape corresponding to the primary molded body is formed by closing the pair of forming molds. A first resin material in a molten state is injected from the first injection unit so as to fill the primary molding cavity and solidified, thereby forming the primary molded body. Then, the pair of forming molds are separated from each other by a predetermined distance, namely, a so called core-back operation is performed, thereby forming a secondary molding cavity between a cavity surface of the at least one of the pair of forming molds and the primary molded body. A second resin material in a molten state is injected from the second injection unit so as to fill the secondary molding cavity and solidified, thereby forming the secondary molded body inside the secondary molding cavity. Thus, the two-color molded article comprising the secondary molded body superposed on the primary molded body is produced.
In the above-described apparatus, the secondary molding cavity is formed by the core-back operation of the pair of forming molds. Therefore, the surface of the secondary molded body remote from the primary molded body necessarily has the same shape as that of the surface of the primary molded body on which the secondary molded body is superposed. As a result, when the above-described apparatus is used, the overall shape of the obtained two-color molded article depends on the shape of the primary molded body, and it is therefore impossible to obtain a two-color molded article having a shape different from that of the primary molded body.
Further, in the above-described apparatus, the pair of forming molds is provided with a slot for injecting the molten resin into the secondary molding cavity, and the pair of forming molds is opened after the core-back operation. Namely, the pair of forming molds is configured so as to successively conduct the primary and secondary injection molding operations. Therefore, it was generally impossible to obtain the primary molded body as the end product by a single primary injection molding operation without a secondary injection molding operation by using the above-described apparatus. Even if it was possible to do so, unnecessary operations such as the core-back operation for molding the secondary molded body should be performed just to obtain the primary molded body.
In other words, the conventional apparatus for producing the two-color molded article, which is configured such that the at least one of the first and second injection units is attached to the pair of forming molds, is intended to be used only for the production of the two-color molded article. It was not possible to use the apparatus as a general injection molding apparatus for producing the molded article by a single primary injection molding operation. Even if it was possible to do so, the productivity of the molded article was insufficient to practically use the apparatus as the injection molding apparatus for producing the molded article by the single primary injection molding operation. The conventional apparatus for producing the two-color molded article, which is configured such that the two injection units are disposed separately from the two pairs of forming molds, is also used only for the production of the two-color molded article. Its structure does not substantially permit the use of the apparatus for both purposes of producing the two-color molded article and producing the molded article by the single primary injection molding operation.